1. Field of the Invention
The present invention relates to a series of pyridazinone compounds, a process for their preparation, compositions containing these compounds, and a method of regulating the growth of plants using such compounds.
2. Description of the Prior Art
Although genetic manipulation of plants through cross-breeding is a well-known process, hybrids of self-pollinating plants had been difficult to produce. In some cases, e.g., corn, intensive hand labor is required to prevent self-pollinating but is possible because the male and female flower parts are distant from each other on the corn stalk. However, in other plants, e.g., wheat, the male and female plant parts are contained within the same flower and self-pollination is difficult if not impossible to prevent. In wheat, the male stamen produces pollen inside a closed flower. The pollen then falls within the closed flower onto the female stigma. Only after this self-pollination step does the flower open to release extra pollen. Mechanical prevention of self-pollination as is practiced in corn is accordingly impossible in a plant such as wheat.
Nevertheless, it is possible to inhibit self-pollination in wheat and similar plants by chemically inhibiting the formation of pollen or by inducing the plant to produce non-functioning pollen. Several compounds have previously been developed which produce these effects.
DOS No. 28 08 795 discloses compounds of the formula: ##STR3## in which R.sup.1 is carboxy, a carboxy salt, or an alkoxy carbonyl group, R.sup.2 is a substituted phenyl group, R.sup.3 is alkyl, and R.sup.4 is hydrogen, alkyl or halogen. These compounds are disclosed to be pollen suppressants.
Published European patent application No. 0 037 133 discloses compounds of the formula: ##STR4## in which X represents oxygen or sulfur, Y represents hydrogen, halogen or an alkyl group, Z represents an alkyl group, Ar represents an optionally substituted phenyl group, and R represents a group which may be, among others NR.sup.1 R.sup.2 or ONR.sup.1 R.sup.2 in which R.sup.1 can be hydrogen and R.sup.2 can be an alkoxy group, an acyl group derived from a carboxylic or carbamic acid, or an alkyl group substituted with a carboxylic acid or ester group. These compounds are also disclosed to be pollen suppressants.
Published European patent application No. 0 049 971 discloses compounds of the formula: ##STR5## in which R.sup.1 can be phenyl substituted with a halogen, R.sup.3 can be carboxy or an alkali metal salt thereof, an alkoxy carbonyl, or a substituted carbamoyl, R.sup.5 is a carboxy derivative of the type defined for R.sup.3, and R.sup.6 is a C.sub.1 -C.sub.4 alkyl group. These compounds are disclosed to be chemical hybridizing agents which operate by causing male plant sterility.
Nevertheless, many of these compounds have adverse affects on hybrid seed quality or injure plants at doses only slightly above those required to produce maximum male plant sterility. Accordingly, a continued need for new pollen suppressants useful for producing hybrid seed of cereal grain exists.